The present invention relates to an improvement in a so called wet process for preparing uranium tetrafluoride by reacting a uranous solution with a hydrofluoric acid solution.
Uranium tetrafluoride is important as an intermediate product in a process for preparing uranium hexafluoride or metallic uranium from a uranium concentrate (yellow cake).
In a wet process for the preparation of uranium tetrafluoride, a uranous solution and a hydrofluoric acid solution are introduced into a fluorination precipitation tank and these solutions are reacted with each other in the tank to form a precipitate of uranium tetrafluoride crystals.
As an example of the conventional wet process for the preparation of uranium tetrafluoride, there is a process proposed in U.S. Pat. No. 4,062,923. This prior art process is illustrated in FIG. 2. When a uranous solution and a hydrofluoric acid solution are supplied to the lower part of a fluorination precipitation tank 1 by means of a pump, crystals of uranium tetrafluoride are formed in the tank. The crystals are caused to rise by propeller-shaped agitation blades 2 disposed in the lower portion of the tank, and floated up by the action of a horizontal swirling stream induced by a plate-shaped agitation blade 3 disposed above the propeller-shaped agitation blades 2. During the floatation, the crystals grow and enlarge in a reaction zone 4 inside the tank 1, and finally precipitate. The precipitated uranium tetrafluoride crystals are discharged in the form of a slurry from a discharge pipe 5 arranged at the bottom of the tank, while the reaction mother liquor is separated from the crystal particles in a solid-liquid separation zone 6 located in the upper portion of the tank and is dischaged as a waste liquid from an overflow pipe 7. The liquid temperature in the tank is maintained within a range from about 90.degree. C. to the boiling point of the liquid by a heater 8. By this prior art process, the uranium tetrafluoride crystals having a relatively large particle size can be continuously prepared.
According to the above-mentioned conventional process, in order to attain enlargement of the uranium tetrafluoride crystals, the crystals are gradually grown at a solution concentration of a low degree of supersaturation in the reaction zone 4 where the hydrofluoric acid solution contacts with the uranous solution. Accordingly, solutions each having a low concentration are supplied to the fluorination precipitation tank 1 so as to attain a low degree of supersaturation. Therefore the amount of the supplied liquid is increased as compared with the manufacturing capacity and the reaction time is prolonged so that the size of the fluorination precipitation tank has to be increased. As a result, the quantity of heat required for heating the liquid within the tank is increased and the amount of the waste liquid discharged from the tank increases. Thus, the above-mentioned conventional process is economically disadvantageous in various points.
Furthermore, in order to perform separation of crystal particles from the waste liquid at a high efficiency in the soild-liquid separation zone 6 disposed in the upper portion of the tank 1, it is necessary to control the agitation speed in the reaction zone 4, and since the size of the tank 1 is large, the liquid in the tank becomes heterogeneous and it is impossible to prevent formation of fine crystals reliably.
Moreover, since the solid concentration in the slurry discharged from the bottom portion of the fluorination precipitation tank 1 is high, clogging is often caused in the discharge pipe 5 and a problem arises with respect to the operation safety.